Silent energizing device for use with fluorescent lamp assemblies



March 13, 1951 B. K. NASTER 2,545,163

SILENT ENERGIZING DEVICE FOR USE WITH FLUORESCENT LAMP ASSEMBLIES Filed May 28, 1948 wag/4v.

Patented Mar. 13, 1951 UNITED STATES PATENT OFFICE SILENT ENERGIZIN G DEVICE FOR USE WITH FLUORESCENT LAMP ASSEMBLIES Bert K. Naster, Chicago, 111.

Application May 28, 1948, Serial No. 29,898

2 Claims. 1

My invention relates to a silent energizing device for use with a fluorescent lamp assembly oi the type having a reflector including magnetic elements.

In conventional fluorescent lamp assemblies, an energizing inductor or ballast is rigidly held in a cup-shaped sheet steel housing by pitch or other suitable pottin compound. This housing is spot welded or otherwise attached to a sheet steel light reflector which, in turn, supports the lamp or lamps.

While assemblies of this type possess the desirable characteristics of inexpensiveness, ruggedness, and simplicity, they are subject to the disadvantage that leakage flux from the induc tor threads the reflector and housing. This time varying magnetic flux causes corresponding movements of the parts or" the assembly to generate an audible hum which may be heard by persons in the vicinity. The annoyance associated with this sound is increased by the reflector itself which acts as a sounding board in creasing the intensity of the sound and directing it towards the user of the light.

In accordance with the present invention, magnetic sheets or plates are snugly fitted about the windings of the energizing inductor or ballast and rigidly attached thereto. The resulting assembly is then rigidly mounted in the conventional housing. The magnetic sheets define flux 5 paths about the inductor and avoid creation of magnetic flux in the housing and reflector. Moreover, the sheets act to increase the leakage flux of the ballast, thereby improving the stability of operation, particularly in the case of b two-lamp ballasts where one lamp is energize through a capacitor or other reactance element.

It is, accordingly, a general object of the present invention to provide an improved energizing device for use with a fluorescent lamp assembly and which produces negligible sound while operating.

Further, it is an object of the present invention to provide an improved silent energizing device for use with a fluorescent lamp assembly and which contributes to the electrical operation of the unit.

It is till another object of the present invention to provide an improved silent energizing device for use with a fluorescent lamp assembly and which aids in evenly distributing the heat within the unit, thereby reducing the temperature spread between the maximum or hot spot temperature in the unit and the average temperature.

Yet another object of the present invention is to provide an improved silent energizing device for use with a fluorescent lamp assembly hav-' ing features of construction, combination, and arrangement rendering it simple in construction and reliable in operation to the end that a unit of minimum cost and maximum utility is provided.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention, itself, however, both as to its organize.- tion and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing in which:

Figure 1 is a top plan view of the device of the present invention;

ure 2 is a top plan view of a complete fluorescent lamp assembl of the type to which the principles of the present invention are appli cable;

Figure 3 is a cross sectional view through the axis 33, Figure 2; and

Figure 4 is a circuit diagram of a fluorescent li hting system of the type to which the principles of the present invention are applicable.

Referring now to the drawing, there is shown at If) the core of a conventional core-type transformer for energizing a two-lamp fluorescent lamp assembly. Core i0 is of rectangular shape and. has a rectangular window defining a pair of legs about which the windings l2, l4, l5, I8, :20 and 22 are wound. Preferably these windings are wound about suitable insulating bobbins into which the leg forming portions of core iii are inserted.

The core Ill is preferably made of a plurality of lamination of silicon steel or other low loss magnetic material.

Insulating spacers 24 and 26 hold the windings in position relative to core l2.

The assembly comprising core it and the coils mounted thereon is received in the channel shaped insulating spacer 28 which is best seen in the cross sectional view of Figure This spacer is likewise received in the channel shaped soft iron member 33. An auxiliary fiat plate 35 of soft iron rests against the bottom of the member 30.

A flat plate 32 of soft iron is positioned against the windings on the open side of channel shaped member 30.

The assembly comprising core l0, coils 12 to 22, and plates 30, 32, and 36 is held together by cotton tape 34 which is wrapped as indicated in Figure 1. Upon completion of the wrapping process, the tape 34, together with the coils, is impregnated with varnish or tar compound to form a complete unitary assembly upon hardening or drying. This prevents vibration of the soft iron plates 30, 32, and 36 relative to core H1 or to each other.

The unitary assembly formed as above described is encased within channel-shaped housing 38, Figure 3, by pitch or other suitable potting compound 39. This compound rigidly holds the assembly in fixed position relative to the housing 38.

The channel-shaped housing 33 is mounted on the reflector 42 by spot Welding or other suitable means. In the particular construction shown in Figure 3, the housing 38 is spot welded to the upturned ears of the plate 4| which, in turn, is spot welded to the upper surface of the reflector 42.

As indicated in Figure 3, the reflector 42 is inverted dish shaped in cross section and includes a downwardly extending skirt portion 42a. Spaced socket members 44 and 46 depend downwardly from this reflector and receive the fluorescent lamps 48 and 50.

The reflector 42 directs light from lamps 48 and 50 in the downward direction. The skirt portion 42a of the reflector forms a shield hiding these lamps when viewed from the side.

Figure 4 shows the circuit. connections of the complete lamp assembly. As indicated, a source of alternating voltage is connected to the primary windings 20 and i5, thereby creating a time varying flux in core Ii! in accord with the voltage of source 52. This time varying flux induces voltage in coils 22 and I4, which, together with the voltage of source 52, is applied to fluorescent lamp 48. Similarly, the voltage induced in coils l8 and I2 is applied to lamp 50 through the ca pacitor 58 and resistor 63.

The lamps 48 and B are started by switches 54 and 56 which selectively energize the filaments 48a and 481) or 50a and 531).

When the primary windings 22 and i4 are energized to light lamps 48 and 50, a time varying flux is established in core 0. This flux also follows any available leakage flux paths, which, in the absence of plates 30, 32, and 36, include portions of the reflector 42 and housing 38.

Heretofore, the leakage flux in reflector 42 and housing 38 has been sufliciently great to cause considerable vibration of these members. This vibration produces sound which is made more intense and more annoying by the sounding board effect of the reflector 42. However, in the improved unit of the present invention, the leakage flux is confined to the soft iron plates 32, 30, and 36 which are formed in a unitary structure with the core l0 and windings l2, I4, l6, I8, 20, and 22 and which define leakage flux paths in dependent of the housing 38 and reflector 42. Thus, there is no tendency to impart vibrations to the reflector 42 and a silent unit is provided.

The magnetic plates 32, 30, and 36 also define additional flux leakage paths about windings I2, l4, l6, I8, 20, and 22, thus causing the voltampere characteristic of the ballast to droop at a greater rate than would otherwise be the case. This is very advantageous since the lamps 43 and 50 have the typical arc-type volt ampere characteristic of negative slope. Moreover, in the two-lamp transformer type ballast, such as that shown in Figure 4, I have found that the lamp connected to the phase shifting capacitor 58 starts much more readily when the plates 39, 36, and 32 are provided.

The soft iron plates 32, 39, and 36 have the further advantage of providing good thermal conductivity about the winding and core assembly. This reduces the temperature spread between the hottest spot in the unit and the average temperature and thereby permits higher average temperature and, hence, wattage output without exceeding permissible hot spot temperature limitations.

In this specification and the accompanying claims, I have used the term magnetic to refer to a material, such as soft iron, having high magnetic permeability. Moreover, I have used the term inductor to represent an inductance, transformer, or other similar flux producing device used as an impedance element in the energizing circuit to one or more fluorescent lamps.

While I have shown herein a magnetic reflector 42, it will be understood that only a portion of the structure formed by housing 38, plate 4|, and reflector 42 need be magnetic to produce sound in the absence of the members 30, 32, and 36. I have, accordingly, used the term magnetic elements capable of imparting vibrations to said reflector to designate a unit of this type even though the reflector itself is made of non-magnetic material and only acts as a sounding board.

While I have shown a particular embodiment of my invention, it will, of course, be understood that I do not wish to be limited thereto since many modifications both in the parts themselves and their cooperative structure may be made Without departing from the spirit and scope of my invention. I, of course, contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my I invention. I

I claim as my invention:

1. In a fluorescent lamp assembly having a reflector formed at least in part of ferrous metal, an energizing device for the fluorescent lamp comprising an iron core, an inductance coil Wound thereon, a plurality of flux-trapping plates disposed on external surfaces of said coil, a casing for said assembly, said casing being mounted on the reflector, and inelastic means comprising pitch or like material suspending said core, coil, and flux-trapping plate assembly within said casing, said flux-trapping plates being operative to confine the leakage flux and thus prevent magnetically induced vibrations in said casing and reflector, and said inelastic suspending means being operative to prevent mechanical transmission of vibrations from the flux-trapping plates to said casing and reflector.

2. In a fluorescent lamp assembly having a reflector formed at l ast in part of ferrous metal, an energizing device for the fluorescent lamp comprising an iron core, coils wound thereon, a flux-trapping magnetic shield formed of magnetically permeable material and surrounding the external surfaces of said coils to trap and confine the leakage flux therefrom, a casing for said assembly, said casing being mounted on the reflector, and inelastic means comprising pitch or like material suspending said core, coils, and flux-trapping shield within said casing, said flux-trapping shield being operative to prevent magnetically induced vibrations in said casing and reflector, and said suspending means being operative to prevent mechanical transmission of vibrations to said casing and reflector from said flux-trapping shield.

BERT K. NASTER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Horn May 6, 1941 Wilson June 2, 1942 Curtis July 7, 1942 Scribner Dec. 28, 1943 Biller Feb. 22, 1944 Ainsworth Apr. 18, 1944 Howe Nov. 13. 1945 

